Servo brake mechanism



Aug. 12 1941. GATES 2,252,482

SERVO BRAKE MECHANISM Filed July 15, 1957 5 sheets-sh et 4 Aug. 12, 1941. 2,252,482

G. R. G. GATES SERVO BRAKE MECHANISM Filed July 15, 1937 5 Sheets-Sheet 5 N Q N ATTOQ/VEYS Patented Aug. 12, 1941 SERVO BRAKE LIECHANISM Geoffrey Robert Greenbergh Gates, London, England, assignor of one-half to Automotive Products Company Limited, London, England Application July 15, 1937, Serial No. 153,846 In Great Britain July 15, 1936 17 Claims.

This invention relates to servo brake mechanism of the type in which a servo or booster device is brought into operation by the actuation of a foot pedal or the like, the brake-applying effort being transmitted to the brake hydraulically or mechanically.

My patent, No. 2,096,396, dated October .19, 1937, describes booster brake mechanism of this kind employing a clutch booster having a continuously rotating driving member or members and one or more driven members connected operatively with the brakes and comprising, in combination with the booster clutch, the usual brake pedal and connection for operating the brakes therefrom, and hydraulic mechanism for operat ing the booster from the brake pedal, the cylinder and ram of which hydraulic mechanism are actuated by movement of the brake pedal to create fluid pressure for operating the booster, this fluid pressure being reduced by the operation of the booster in applying the brakes. The specification describes the arrangements in which the cylinder and ram of the hydraulic mechanism for operating the booster or servo serve not only to produce liquid pressure in said mechanism but also to reduce said pressure upon the operation of the servo. According to the present invention, however, reduction of liquid pressure in a hydraulic system for operating the booster of the brake mechanism is effected by cylinder and piston structure.

One object of the present invention is, therefore, to provide a hydraulic system for operating the booster of a brake mechanism of this type which includes cylinder and piston structure so arranged that the greater the efiort applied to the brake pedal the greater the volume of the cylinder and piston structure.

As another object, the invention seeks to provide a brake system employing a master cylinder operated by a foot pedal or the like, the pressure in which acts to bring the booster into operation, the pressure being reduced in the cylinder as the booster comes into action by the increase of volume within an additional piston and cylinder structure connected with the system, the variation of depressed efiort on the pedal serving to vary the extent of operation of the booster.

As a still further object, the invention seeks to provide a fluid pressure system employing a booster having a master cylinder operated by a foot pedal, and a plurality of additional or slave cylinders acting to bringthe booster into operation as well as an additional cylinder and piston type variable volume device, all of the structure acting to set up a state of balance between the depressed effort on the pedal or the like and the effort exerted by the booster.

Further and incidental objects of the invention not specifically mentioned herelnbeiore will become apparent during the course of the following description.

The invention is lllustrated in the accompanying drawings, wherein Figure 1 is a diagrammatic view showing 'a clutch type booster device wherein the brakeapplying eiiort is transmitted hydraulically to the brakes,

Figure 2 is a diagrammatic view showingthe same arrangement applied to a system wherein the brake-applying effort is transmitted mechanically to the brakes,

Figure 3 is a diagrammatlcview showing an arrangement having a vacuum type booster and a valve controlling the connection thereof with a source of reduced pressure, the valve and booster being shown in section,

Figure a is a sectional view of a cylinder containing both a variable volume piston and a slave piston,

' Figure 5' is a sectional view, partly in elevation showing a practical booster device as it will appear operatively connected with brake-applying means, the brake pedal or other manual control, the hydraulic pressure-creating'means and the hydraulic connections being omitted,

Figure 5a is a fragmentary sectional view disclosing the mounting for the slave cylinders and their associated parts.

Figure 6 is a horizontal sectional view, partly in elevation, showing a modified arrangement of booster,

Figure 7 is a longitudinal sectional view showshowing a still further modified booster structure, and

Figure 8 is a vertical sectional view on the line 8-8 of Figure 7 looking in the direction indicated by the arrows.

Referring now more particularly to the drawings wherein similar reference numeralswill be V seen to designate like parts throughout the various views, reference is had particularly to Figure 1 wherein a master cylinderproducing a hydraulic pressure by which braking pressure is transmitted to the brakes, is indicated generally at H, and the connections thereto of the brake leads or conduits at 12. In this example, a closed space i3 is provided behind the master piston l4 and is utilized as an additional variable volume device.

As will be seen, the space l3 is connected by a pipe IS with a pedal master cylinder |6, which includes a piston ll therein which piston is adapted to be connected with a brake pedal l8 for movement thereby. The cylinder I6 is connected, also, by a pipe l3 to a slave cylinder 20 which will be effective for operating the booster clutch device shown generally at 2|. It should be understood that, if desired, more than one slave cylinder may be employed. The driven member or members of the booster clutch 2| are connected to an arm 22 which is connected by means of a rod 23 with the master piston l4.

As will be understood, when the brake pedal I3 is depressed, pressure is created in the pedal cylinder l6, in the pipes l5 and is, in the space It, and in the slave cylinder 20, with the result that the servo or booster device 2| is caused to shift the master piston H to create pressure in the cylinder I I for increasing the volume of the space l3 and reducing the pressure in the cylinder l6 whereby operation of the booster is maintained. As will be seen, there is established a balance between the pressure within the master cylinder H i. e., the actual brake-applyin effort on the one hand and the pressure in the pedal cylinder It on the other hand so that the booster 2| will always be under control of the driver by way of the pedal l8. Attention is directed to the fact that even in the event of failure of the booster 2|, the brakes can still be applied by the brake pedal without the assistance of the booster for the reason that, if the booster is inoperative, the

pressure in the cylinder l3 will be transmitted to Referring now to Figure 2 of the' drawings,

wherein braking mechanism in which the braking effort is transmitted mechanically to the brakes, as shown, there is connected with the arm 22 of the booster 2|, instead of the rod 23, a rod 24 which extends through a cylinder 25 and has secured thereon a piston 26, the rod 24 extending past the piston and through the cylinder and having secured at the end thereof a lever 21 which has its opposite end connected with a cross shaft 23, which cross shaft is connected mechanically with the brakes by means of tie cables 23 and 30. In this embodiment of the invention, the conduit l5 will be connected with the cylinder 25 instead of with the space l3 behind the master piston. It will be understood that the cylinder 25 is equivalent in every respect to the space l3 of Figure l, the only difference in operation between the two arrangements being that, in one case, the applying pressureis transmitted hydraulically and in the other case mechanically to the brakes.

Referring now to Figure 3 of the drawings, a piston 3! has a thrust rod 32 extending therefrom. The piston 3| constitutes the master piston of a master cylinder 33 which is connected by a pipe 34 with the brakes. The rod 32 is connected, at its outer end, with a lever 35 which is pivoted at 36 and which is connected at its lower end with a piston 31 which operates in the cylinder 38. The piston 31- and cylinder 33 constitute a vacum type booster device and, as will be seen, reduction of pressure in the cylinder 33 will aseaeaa cause shifting of the piston 31 and rocking of the lever 35 for imparting effort to the piston 3|. The space behind the piston 3| is enclosed to define a variable volume cylinder 33 which is connected by suitable passages and a pipe 40 with a pedal cylinder 4|. The piston 42 within the pedal cylinder is connected with a brake pedal 43 and is actuated thereby. The pedal cylinder also may be connected by a pipe 44 with a single slave cylinder 45. As will be seen, the cylinder 38 is normally open to the atmosphere by virtue of the pipe 46, the interior of the valve 41 and included valve structure. The valve chest or interior 41 is formed with a valve seat 50 which normally cooperates, by means of a spring 5|, with a valve 52 having an integral stem 53 slidable within the sleeve 43 of the valve. The stem is formed with a plurality of slots 55 which afford communication for air through ports 43 and the interior of the sleeve 48. A blank 56 communicates between the valve chest 4'! and a source of reduced pressure such as the intake manifold of an internal combustion engine. The sleeve 48 is formed with an integral flange 51 and with a stem 58 extending coaxially therefrom into a recess 53 in an enlarged head 50 of a piston 6| of the slave "cylinder 45. A spring 62 surrounds the sleeve 48 between the flange 51 thereof and the adjacent end of the valve chest 41. A further compression spring 63 surrounds the stem 58 between the flange 51 and the adjacent end of the head 63 of the piston or plunger 6|. It will be seen that, when the pedal 43 is depressed, the pressure in the slave cylinder 45 shifts the plunger or piston 6|, thus compressing the spring 63 until the spring 62 is flexed, when the sleeve 48 will be shifted inwardly until it abuts against the valve 52, thus cutting off the cylinder 33 from the atmosphere. As the movement of the sleeve continues, the valve 52 is displaced from the valve seat 50 for placing the cylinder 33 in comniunication with the pipe 56 and thus with the source of reduced pressure. The result is that the booster piston 31 is rendered operative and motion is transmitted to the piston 3| for creating pressure within the cylinder 33 and applying the brakes. It should be noted that the more the booster acts in the application of the brakes, the more the volume of the space 39 behind the piston 3| is increased. A-

given increase in the volume of the space 39 will allow the spring 62 to overcome the spring 63 and close the valve '52 for limiting the application of the brakes. The spring 5| is just sufliciently strong to maintain the valve 52 in engagement with the valve seat 50 against the pressure at that side of the valve which is open to the atmosphere. In the event that the booster fails, a stop 64 limits movement of the piston 6| so that pressure from the pedal cylinder 4| may be transmitted to the brakes by the piston 3|.

Attention is directed to the fact that both of the master cylinders H and 33 in Figures 1 and 3, respectively, have recuperation passages 7| which are effective for allowing any excess or deficiency of fluid to be compensated from an external tank 12 at which time the moving parts are located in their inoperative positions. The passages II are in permanent communication with the pedal cylinders I6 and 4|, which also have recuperation passages 13 so that the reservoir or tank 12 will serve for both the hydraulic systems. Therefore, in each case, the booster controlling hydraulic system will be replenished directly from the reservoir or tank 12 and the brake-applying hydraulic system will be replem ished from the "booster controlling system. Any

- excess fluid in the brake system will spill to the booster system andfrom the booster system into the tank 12.

In all the arrangements so far described, the reduction of pressure in the system as the servo operates is effected by the change of volume of what is in fact a separate variable volume device connected with the system, although, in the case of Figures 1 and 3, the variation of volume is effected directly by the movement of the master piston whereby braking effort is transmitted hydraulically to the brakes. It is not necessary, however, that such a separate variable volume device should be employed, for instead one or more slave cylinders may be utilized to eii'ect the reduction of pressure.

As shown in Figure 4 of the drawings, I employ a cylinder 8I which is connected by a pipe 82 with a pedal cylinder, such as the cylinder I5 or 4|. The cylinder 8| contains two opposed pistons 83 and 84. The piston 03 is a slave piston and is connected operatively by suitable means with the booster or with a valve controlling the operation thereof. The piston 84 is operative for controlling the volume between the pistons 83 and 84 and is mechanically connected to move with the booster and may, for example, be equivalent to the piston 25 of Figure 2 or the piston I4 of Figure 1. Thus, in operation, depression of the pedal to operate the pedal cylinder I5 supplies pressure liquid to the space between the two pistons 03 and 34. Movement of the piston 83 will, of course, cause movement of the liquid in the cylinder, and said liquid to be compressed for moving the piston 84. The lever 21 will thus be shifted.

Referring now to Figure 5 of the drawings, I have illustrated a clutch type booster or servo similar to that described in Patent No. 2,096,393. The clutch or booster or serve, as shown in Figure 5, includes a single driving plate Il splined with a shaft I02 which is driven continuously from the conventional transmission of the vehicle preferably so that it rotates with the road wheels of said transmission. The driving plate IOI is positioned between two driven plates I03 and I04, the plate I03 being fixed on the crank shaft I and the plate I04 being rotatable relative to the shaft I02 and slidable in relation thereto and to the plate I03 with which it is caused to rotate by means of pins I05 which extend from the plate I03 through openings in the plate I04. The plate I04 isv centered about the shaft I02 by a disc I0l located in a recessed part I08 of the plate I04 together with a thrust bearing, indicated at I00,

'with which cooperate a number of thrust rods,

one of which is indicated at IIO. Each of these thrust rods I I0 extends into a corresponding slave cylinder, one of which is indicated at III, to cooperate with the piston II2 therein, the casing I I3 of the mechanism being formed with internal I bores, indicated at H40. and Ilia, communicating The cylinder II5 has the brakes, the usual brake pipes being con 'nected with the master cylinder Ill at the ports Ill. The guide block III has extending therefrom an integral thrust rod Ill secured, as indicated at I20, to the piston I2I of the master cylinder Ill. This rod IIO extends through a partition I22 and a gland I23 enclosing a space I24 at the rear of the master piston I2I. The space I24 is connected through the port I25 and union I with the pedal master cylinder Illa.

It will be seen that angular movementof the crank shalt I05 in either direction as the result of the engagement of the clutch will result in movement of the piston I2I to create brake-applying pressure in the master cylinder Ill and, at the same time, to increase the volume of the space I24 behind the piston I2l, thusreducing the pressure in the slave cylinder III by which -the clutch is engaged. At the termination of braking the piston I2I, the guide blo'ck H5 and the crank shaft I05 are returned to the normal positions shown by the usual return springs In in the master cylinder Ill and by a spring I28 surrounding the rod IIO.

Referring now to Figure 6 of the drawings, another embodiment of the booster is shown. This arrangement is, essentially, similar to that shown in Figure 5. In this embodiment, however, a shaft I5I, which is driven continuously from the transmission of the vehicle and which is preferably the propeller shaft, is surrounded by a multiple clutch having driving plates I52 which are splined on the shaft I5I and the driven plates I53 which are of larger diameter and are keyed together by pins I54 extending from a driven member or flange I55 which defines an annular groove or channel I55. The clutch of this embodiment of the invention is engaged by the introduction of liquid under pressure from a suitable pedal master cylinder, such as the master cylinder hereinbefore described, by way of ports l5l to a plurality of slave cylinders, two of which are shown at I58, which contain pistons I50 cooperating with a thrust member I60. The master cylinder I5I in this instance is disposed parallel with the axes of the clutch I52, I53 and has a thrust rod I52 extending from the rear face of the piston thereof through a partition and gland which are similar to the piston and gland I22 and I23, respectively, of the arrangement shown in Figure 5; this rod I62 being surrounded by a return spring I53. At the end remote from the master cylinder I5I, the rod I62 cooperates with a member I54 in splined relationship with a cylinder I55 through which the rod I62 extends and which carries the master cylinder I5I. The member I54 has a portion I55 which is formed with a quick pitch screw thread I61. A rotatably mounted axially fixed nut I68 cooperates with the thread part I55 of the member I64, and this nut is formed with an annular groove or channel I50. A roller chain, shown in dotted lines at I10, serves to transmit motion from the driven clutch member I55 to the nut I68, the chain being anchored at one end to a pin IlI which extends across the groove I55 in the driven member I55 and is similarly anchored at its other end to the nut I50,

The chain I10 is so disposed relative to the clutch member I55 and to the nut I58 that movement of the driven member in either direction will rotate the nut I58 and, therefore, shift the member I04 to the right, as shown in the draw ings, Thus, by means of the rod I62, the master piston will be shifted to create brake-applying effort or pressure. After braking, the nut I88 is returned to the normal position shown by the usual return springs in the master cylinder I66 and by the spring I53. In this case, however. the driven clutch member I55 is returned to its normal position by a slight'drag on the clutch I52, I53 to produce which drag I provide springs I12 in the slave cylinders I58. This drag in the clutch I52, I53 takes up lost motion in the connection between the driven member I55 and the nut I68, and insures that the master piston shall be shifted immediately upon actuation of the brake pedal or other control member.

In view of the fact that large diameter driven clutch members I53 are provided, such members serve efiiciently as cooling fins. In order to assist in cooling, the casing of the device is cut-away, as indicated at I13, where it surrounds the clutch.

The rods I54 have threaded thereover, alternately, coiled compression springs I16 and bushings I so disposed that, between each adjacent pair of clutch plates "I53, each rigid bushing I15 is diametrically opposed to a spring I14. The clutch plates will thus be prevented from vibrating. Attention is called to the fact that only two diametrically opposed rods I54 may be provided with clutch springs I74 and bushings I15, as illustrated.

The embodiment of the invention as shown in Figures '1 and 8 of the drawings is quite similar to that shown in Figure 6. In this embodiment, however, a single cylinder and piston device operate as a slave cylinder and to effect reduction of pressure in the system with booster operation. A shaft 20I, which may be the propeller shaft of the vehicle, carries a clutch 202 which is similar in construction to that shown in Figure 6 and has a driven member 203 connected by a roller chain 204 with an axially fixed nut 205 for imparting pressure through a thrust rod 205 to a master piston 201 for effecting in a master cylinder 208 the necessary pressure for brake application. The rod 206 extends through an annular piston 209 slidable in a rearward extension 2) of the master cylinder 208, a gland or packing 2II being provided to maintain a liquid tight space 2I2 between the pistons 201 and 209. A fork 2I3 cooperates with the rear face-of the piston 209 and said'fork is integrally formed with a cross shaft 2M. The cross shaft 2 has formed integrally thereon an additional fork formed with arms 2I5 which cooperate with a thrust bearing 2I6, the thrust bearing engaging and operating the clutch 202.

The space 2I2, between the pistons 201 and 209, is connected by a pipe 2I1 with a pedal cylinder similar to that shown and described drawings are applicable in cases where-the brakeapplying effort is to be applied mechanically in.- stead of hydraulically to the brakes. For exampie, in Figure 5, the rod II9 may extend through and beyond the piston I2I to be connected with the mechanical brake mechanism.

It is thought that the construction and operation of my improved system will now be clearly understood.

Having thus described the invention, what is claimed as new is: i

1. In a system of the class described, a pedal cylinder, 9. foot pedal operatively connected therewith, a-booster, a slave cylinder operatively connected with the booster effecting operation of the booster upon depression of the foot pedal, and an additional cylinder and piston device adapted to have the volume thereof increased by operation of the booster, the liquid required to fill the increased volume. being withdrawn from the system, thus reducing pressure in the system and balancing the depressive eifort on the pedal with the effort exerted by the booster.

2. In a hydraulic fluid pressure system, a master cylinder, a piston, a booster, means operatively connecting the booster with the piston, brakes, a rod connected with the brakes and extending concentrically into the master cylinder for connection with the piston therein whereby said ,brakes will be mechanically connected to the cylinder and piston, the volume of the cylinder being increased at one side of the piston as thebrakes are applied by operation of the booster and said piston.

3. In a-hydraulic system of the class described, in combination with vehicle brakes, a brake pedal,

a cylinder operatively connected with the brake 7 adapted to flow through the pedal cylinder back hereinbefore, and it will be seen that pressure in the space 2I2 will shift the piston 209 for rocking the shaft 2M and transmitting pressure to the bearing 2I6 for engaging the clutch 202. The operation of the clutch shifts the piston 201 for reducing the pressurein the space 2 I2 and thus reducing the pressure applied to the bearing 2I6. When the pressure from the pedal cylinder is released, the piston 209 is caused to assume a normal position by the action of a resilient washer 2 I8 which is engaged in a circumferential groove 2 I9 in the rearward extension 2I0 of the master cylinder 208. At its inner periphery, the washer engages in a circumferential groove 220 formed in the rear portion of the piston 209.

It will be readily understood that the booster to the reservoir.

4. In a hydraulic system of the class described, in combination with vehicle brakes, a pedal, a hydraulic cylinder unit operated thereby, a variable volume device connected hydraulically with the pedal cylinder, a motor cylinder unit also connected hydraulically with the pedal cylinder, a booster controlled by the motor cylinder unit 'and operatively connected with the brakes, said booster being of the clutch type and having a crank and driving and driven members, a thrust rod shiftable by the crank, said crank being adapted to turn with the driven members, a connecting rod connected with said thrust rod and being adapted to be moved by the connecting rod in the same,- direction when the crank is' moved, a master cylinder having a piston, said piston being fixed on the thrust rod, said 'rod and piston moving for transmitting hydraulic brake-applying effort to the brakes while operaarrangements shown in Figures 5 to 8 of the tion of the booster causes the variable volume device to become enlarged, thereby tending to reduce the liquid pressure in the motor cylinder unit.

ing the pressure in the system and operating the booster in accordance with depressive effort on the foot pedal, the volume of the variable volume device being increased progressively with decreasing volume in the system and consequent increased effectiveness of the booster.

6. Asystem for operating booster brake mechanism including a foot pedal, 9, liquid pressure generator operated by said foot pedal, 9, master cylinder, a booster, a piston in the master cylinder operated by the booster for supplying hydraulic pressure to the brakes for operating said brakes, said master cylinder being enclosed behind the piston for defining a variable volume device, a motor piston in said variable volume device, and a mechanical connection between the motor piston and the booster, the liquid pressure generator being adapted to supply pressure liquid to said variable device to move said motor piston and operate the booster.

'7. A system for operating booster brake mechanism including a foot pedal, means connected with the foot pedal for creating liquid pressure in the system upon the depression of the pedal, a motor device fed with the pressure liquid-to apply the booster, and a variable volume device hydraulically connected with the pressure creating means and the motor device and actuated by the booster so that as the latter comes into operation the volume of the variable volume device increases, the liquid required to fill the increased volume being withdrawn from the system, thereby reducing the liquid pressure in the motor unit.

8. A system for operating booster brake mechanism including a foot pedal, means connected with the foot pedal for creating liquid pressure in the system upon depression of the pedal, a motor cylinder fed with said pressure liquid, a

' motor piston in said cylinder arranged to actuate the booster, and an auxiliary piston which is also in said cylinder and is connected operatively with the booster so as to be moved by the latter in a direction away from the motor piston as the said booster comes into action, thereby tending to reduce the liquid pressure acting upon the motor piston.

9. A system for operating booster brake mechanism including a foot pedal, means connected with the foot pedal for creating liquid pressure in the system upon depression of the pedal, a motor device fed with pressure liquid to apply the booster, and a variable volume device which comprises a cylinder and piston unit hydraulically connected with the pressure creating means and with the motor device, said variable volume device being actuated mechanically by the booster so that as the latter comes into operation, the volume of the variable volume device increases, the liquid required to fill the increased volume being withdrawn from the system, thereby reducing the liquid pressure in the motor unit.

10. A system for operating booster brake mechanism comprising a foot pedal, a hydraulic cylinder and piston unit actuated by said pedal, a motor cylinder unit connected with the pedal cylinder and arranged to actuate the booster when fed with pressure liquid from the pedal cylinder unit, and a variable volume device comprising a cylinder separate from but hydraulically connected with the pedal cylinder unit and the motor cylinder unit, and a piston insaid cylinder, said piston being mechanically actuated by the booster so as'to increase the working space of the variable volume chamber, the liquid required to fill the increased volume being withdrawn from thesystem, thereby reducing the liquid pressure acting in the motor cylinder unit. I

11. A system for operating booster brake mechanism comprising a foot pedal, a piston and cyldevice comprising a cylinder which is connected hydraulically with the pedal cylinder and the motor cylinder, and a piston which is mechanically connected with the booster so as to enlarge the working space within the cylinder as the master cylinder unit is operated.

12. A system for operating booster brake mechanism comprising a foot pedal, a piston and cylinder unit operated thereby, a motor cylinder fed with pressure liquid from the pedal cylinder and arranged to bring the booster into operation, a hydraulic master cylinder unit including a piston operated by the booster for applying a set of hydraulic brakes, said master cylinder unit incorporating, behind the said piston, a closed variable volume space which is connected with the pedal cylinder unit and the motor cylinder whereby advancing movement of the piston causes the variable volume space to be enlarged thus tending to reduce the liquid pressure in the motor cylinder.

13.- A system for operating booster brake mechanism comprising a foot pedal, a piston and cylinder unit operated thereby, a' motor cylinder fed with pressure liquid from the pedal cylinder and arranged to bring the booster into operation, a hydraulic master cylinder unit operated by the booster for applying a set of hydraulic brakes, a common reservoir feeding the pedal cylinder unit and the master cylinder unit with working liquid, and a variable volume device incorporated in said hydraulic master cylinder unit and comprising a cylinder which is connected hydraulically with the pedal cylinder and the motor cylinder, and a piston which is mechanically connected with the booster so as to enlarge the working space within the cylinder as the master cylinder unit. is operated.

14. A system for operating booster brake mechanism comprising a brake pedal, a cylinder operatively connected with the brake pedal and having a recuperation passage, a reservoir, means operatively connecting the reservoir with the pedal cylinder through said recuperation passage, a master cylinder having a recuperation passage, means operatively connecting the master cylinder recuperation passage with the pedal cylinder whereby said reservoir serves to replenish both of the cylinders, a booster, a motor unit fed with pressure liquid from the master cylinder to bring the booster into action, means operatively connecting the booster with the master cylinder, and a variable volume space which is disposed behind the piston in the master cylinder and is caused to increase in volume as the booster comes into action, thereby tending to reduce the liquid pressure in the motor unit.

15. A system for operating booster brake mechanism including a foot pedal, means connected with the foot pedal for creating liquid pressure in the system upon the depression oi the pedal, a booster of the friction clutch type arranged to be operated from a rotating member such as a shaft, 9. motor device fed with pressure liquid from the pedal-operated means to apply the booster, and a variable volume device hydraulically connected with the pressure-creating means and the motor device and actuated by the booster so that as the latter comes into operation the volume of the variable volume device increases, thereby tending to reduce the liquid pressure in the motor unit.

' 16. A system for operating booster brake mechanism comprising a foot pedal, a piston and cylinder unit operated thereby, a booster of the friction clutch type arranged to derive-brakeapplying force from a rotating member such as a shaft, a motor cylinder unit adapted to bring the booster into operation, said motor cylinder unit being fed with pressure liquid from the pedal cylinder, a hydraulic master cylinder unit operated by the booster for applying a set of hydraulic brakes, and a variable volume device comprising a cylinder which is connected hydraulically with the pedal cylinder and the motor cylinder and a piston which is mechanically connected with the booster so as to enlarge the working space within the cylinder as the master Y cylinder unit is operated.

17. A system for operating booster brake mechanism, comprising a foot pedal, a piston and cylinder unit operated thereby, a booster of the friction clutch type arranged to derive brakeapplying force from a. rotating member such as a shaft, a motor cylinder unit fed with pressure liquid from the pedal cylinder and arranged to bring the boosterinto operation, a hydraulic master cylinder unit including a piston operated by the booster for applying a set or hydraulic brakes, said master cylinder unit incorporating, behind the said piston, a closed variable volume space which is connected with the pedal cylinder unit and the motor cylinder unit whereby advancing movement of the piston causes the variable volume space to be enlarged, thus tending to reduce the liquid pressure in the motor cylinder.

GEOFFREY ROBERT GREENBERGH GATE-S. 

